[PATCH] D158574: [AArch64][ELF] Support PAUTH ABI marking

Mon Sep 18 03:36:45 PDT 2023

peter.smith added a comment.

I agree with MaskRay that for an Alpha specification there is no good reason to support both marking schemes in relocatable objects. I wish I had deleted the alternative one rather than moving it to an appendix. I'll note that the spec covers relocatable objects only, it is the platform's decision about executables and shared objects.

The encoding difference between the processor specific note section and the GNU property is minimal. Essentially the GNU property is just wrapping the contents of the NOTE section in a property. At the relocatable object this doesn't make a lot of difference as the (platform/vendor schema-version) does not fit well with any existing GNU property [*] so it would still need custom code to process. At the executable, shared-object level there is more of a benefit for GNU properties as the program header that identifies the program properties can make it easier for the dynamic linker to find the information. It is possible to use the raw notes in relocatable objects but use a program property in the executable.

Internally to Arm there is a discussion on how to do ELF marking in relocatable objects (not executables and shared-libraries), for example do we continue to use GNU properties or do we use something like Arm (or RISCV) build attributes. I hope that there will be a proposal that can be shared externally for public comment can be put on the Arm ABI github page at some point in the near future. As ABI work tends to move slowly I suspect it will be too late for this though.

[X] X86 and AArch64 properties

X86 properties https://gitlab.com/x86-psABIs/x86-64-ABI/-/merge_requests/13/diffs?commit_id=b0b0c518c28be848e8494bf3dff2a97688e5fce0  
Arch64 properties in https://github.com/ARM-software/abi-aa/blob/main/aaelf64/aaelf64.rst#62program-property

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